Automatic blackboard eraser

ABSTRACT

A device for automatically erasing a blackboard wherein a carriage is mounted for longitudinal movement on the blackboard and has a motor mounted thereon that is mechanically interconnected to a drive assembly for producing the movement of the carriage and also is interconnected to brush means for the rotation thereof during movement of the carriage in an erasing operation.

United States Patent [111 3,858,265

Schlick Jan. 7, 1975 [54] AUTOMATIC BLACKBOARD ERASER 3,254,355 6/1966 Shavv 1 15/1.? Inventor: Rolland L. Schlick, 75 Pa S 3,731,335 5/1973 Chnsp 15/97 R A l b ,M .0270 I tt e om ass 3 Primary ExammerHarvey C. Hornsby [22] Filed: Jan. 15, 1973 Assistant ExaminerC. K, Moore [21] pp No: 323 437 Attorney, Agent, or FirmSalter & Michaelson [52] U.S. Cl 15/77, 15/49 C, 15/103, [57] ABSTRACT 5/319v 15/34() 32/65 A ClVlC6 for automatically erasing a blackboard [51] Int. Cl A471 11/38 wherein a Carriage is mounted for longitudinal move- [58] Field f Search 5/21 E, 77, 97 R, 98 ment on the blackboard and has a motor mounted 5/319, 340 49 C, 32/65 thereon that is mechanically interconnected to a drive assembly for producing the movement of the carriage 5 7 References Cited and also is interconnected to brush means for the rota- UNITED STATES PATENTS tion thereof during movement of the carriage in an 2,167,296 7/1939 Farmer 35/62 X erasmg Operatlon. 3,163,943 H1965 Bell 15/98 X 10 Claims, 14 Drawing Fi ures 3 Sheets-Sheet 1 Patented Jan. 7, 1975 3,858,265

3 Sheets-Sheet 2 Patented Jan. 7, 1975 3 Sheets-Shem FIGH 1 AUTOMATIC BLACKBOARD ERASER BACKGROUND OF THE INVENTION The invention relates to blackboards and has particular application to a device for mechanically erasing the blackboard.

Improvements in blackboards and chalk for use therewith have occurred over a period of time, but such improvements have not effected the manner in which the blackboard is cleaned or erased. The most common method of erasing a blackboard is to use a hand-held eraser and to manually erase the blackboard as re quired. Cleaning of the blackboard by a damp cloth is, of course, a technique that has long been employed but is only used when immediate use of the blackboard is not required. Some efforts have been made heretofore to improve the materials used in erasers, although such improvements still require manual manipulation of the eraser in the erasing of the blackboard. Some attempts have also been made to mechanize erasers, but these prior known mechanical or automatic blackboard erasers have not been very efficient in use since they included complicated mechanical connections and driving elements. The prior known automatic erasers were not only complicated in construction, but the cost thereof was too high to permit the successful manufacture and sale on a production basis.

SUMMARY OF THE INVENTION The present invention relates to a device for automatically erasing a blackboard and comprises an elongated vertically extending carriage that extends for at least the height of the blackboard and is located out wardly thereof in adjacent relation. The carriage ismounted on'the blackboard for traversing forward and reverse movement in a direction that is longitudinal with respect thereto. Mounted in the carriage are counter-rotating brushes that engage the surface of the blackboard and that are driven by a motor that is also mounted in the carriage for movement therewith. The motor is constantly driven in a single direction; but in order to reverse the direction of movement of the carriage after it has traversed the length of the blackboard, a drive assembly is interconnected to the motor and is responsive to the lateral shifting of a control rod for producing the movement of the carriage in the desired direction. A chalk dust collecting device is incorporated in the carriage and provides for removal of the chalk dust into a collection receptacle as the carriage traverses the length of the blackboard and returns to the rest position thereof.

Accordingly, it is an object of the present invention to provide an automatic erasing device that is mounted on a blackboard and that upon energizing of an electric motor effectively erases the surface of the blackboard.

Another object of the invention is to provide an electrically operated blackboard eraser that includes counterrotating erasing brushes that engage the surface of the blackboard and that are driven by a motor, the motor being operatively interconnected to a drive assembly which operates to effectively move the brushes in a traversing motion back and forth across the surface of the blackboard.

Another object is to provide an automatic blackboard eraser that is placed in operation by the shifting movement of an operating rod and after automatically traversing the blackboard in an erasing operation returns to a position of rest.

Still another object is to provide an automatic blackboard erasing device that includes a chalk dust collector system that effectively transfersthe erased chalk dust to a removable dust bag.

Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.

DESCRIPTION OF THE DRAWINGS In the drawings which illustrate the best mode presently contemplated for carrying out the present invention:

FIG. 1 is a front elevational view of a portion of a blackboard showing the blackboard erasing device mounted thereon, portions of the housing for the device being removed to show the interior thereof;

FIG. 2 is a side elevational view of the blackboard and erasing device mounted thereon with parts shown in section;

FIG. 3 is a sectional view taken along line 33 in FIG. 1;

FIG. 4 is a sectional view taken along line 44 in FIG. 1;

FIG. 5 is a sectional view taken along line 55 in FIG. 1;

FIG. 6 is a sectional view taken'along line 6--6 in FIG. 1;

FIG. 7 is a sectional view taken along line 77 in FIG. 1;

FIG. 8 is a perspective view of the motor and drive assembly of the form of the invention illustrated in FIG. 1 showing the drive assembly in the position for forward traversing movement thereof;

FIG. 9 is a view similar to FIG. 8and showing the drive assembly in the position for return movement of the erasing device;

FIG. 10 is a front elevational view of the upper portion of the carriage of a modified form of the invention and illustrating the drive motor and drive assembly when the device is located in the position of rest;

FIG. 1 l is a view similar to FIG. 10 showing the location of the drive motor and drive assembly after the operating rod has been actuated to begin traversing movement of the device;

FIG. 12 is a sectional view taken along line 12-12 in FIG. 10;

FIG. 13 is a perspective view of the motor and drive assembly of the modified form of the invention illustrated in FIGS. 10 12 and showing the drive assembly in the position for forward traversing movement thereof; and

FIG. 14 is a view similar to FIG. 13 and showing the modified drive assembly in the position for return movement of the erasing device.

DESCRIPTION OF THE INVENTION Referring now to the drawings and particularly to FIGS. 1 and 2, one form of the automatic erasing device embodied in the present invention is illustrated and is generally indicated at 10. The erasing device 10 is mounted for traversing movement on a blackboard 11 that is fixed on the vertical surface of a wall 12 or the like by an upper horizontal frame 14 and a lower horizontal frame 16. The lower frame 16 also has 'an outwardly extending shelf 18 joined thereto on which chalk is normally located in use of the blackboard 11. The blackboard 11 may be of any convenient construction and/or color and may also be mounted on a portable frame for movement from one location to another, if so desired. Side frames (not shown) are normally secured to the wall 12 and cooperate with the top and bottom frames 14 and 16 for retaining the blackboard 11 in vertical position on the wall 12.

The automatic blackboard erasing device embodied herein includes a carriage generally indicated at 20 that is mounted for traversing movement with respect to the blackboard 11; and for this purpose, an upper horizontal rail 22 and a lower horizontal rail 24 are provided and are secured to the wall 12 or to the frame on which the blackboard is mounted in any convenient manner. As will be described hereinafter, the carriage 20 is movable longitudinally of the horizontal rails 22 and 24 for the length of the blackboard, it being understood that the horizontal rails 22 and 24 are elongated and extend substantially the longitudinal dimension or length of the blackboard 11.

The carriage 20 includes a housing defined by a front wall 26, a top wall 28, and a bottom wall 30 and side walls 32 and 34 that are joined to the front wall 26 and top and bottom walls 28 and 30. Secured to the side walls 32 and 34 at the upper end of the carriage 20 is a bracket 36, and formed on the bracket 36 is a reinforcing portion 38 that acts to prevent deflection of the bracket 36. Mounted on the bracket 36 for rotation with respect thereto are spaced rollers 40 and 42, the rollers 40 and 42 engaging the upper rail 22 for movement thereover. Thus the carriage 20 is suspended from the rollers 40 and 42 and is movable therewith in a traversing movement with respect to the blackboard 11. Fixed to the bottom wall 30 of the carriage housing is a bracket 44 that has a stepped configuration and to which spaced rollers 46 are secured. The axes of the rollers 46 extend in a vertical direction, and the rollers engage a stepped portion of the lower rail 24 in frictional relation and thereby cooperate with the rollers 40 and 42 to provide for movement of the carriage 20 along the length of the blackboard. The rollers 46 also stabilize the lower end of the carriage 20 and act to prevent the carriage lower end from shifting during the traversing movement thereof.

Secured to the side walls 32 and 34 of the carriage housing at the upper end thereof is a vertical plate 48. Mounted on the vertical plate 48 is an electric motor 50 that is electrically connected to a switch 52, the switch 52 being mounted on a cross bar 54 that is'also secured to the side walls 32 and 34 of the carriage housing. The motor 50 is energized by actuation of the switch 52 through a toggle lever 55, as will hereinafter be described. Drivingly interconnected to the motor 50 are a pair of vertically extending brushes 56 and 58, the brushes 56 and 58 being mounted on shafts 60 and 62, respectively, and the shafts 60, 62 being received in bearing relation in an upper support bracket 64 and a lower support bracket 63. As shown in FIG. 2, a shaft 67 of the motor 50 is drivingly connected to the shaft 60 of the brush 56 through a coupling 66. Mounted on the shaft 60 of the brush 56 is a gear 68 that meshes with a gear 70 that is mounted on the shaft 62 of the brush 58, the gears 68 and 70 having a 1:1 ratio. It is seen that the brushes 56 and 58 rotate in opposite directions since thay are directly interconnected through the gears 68 and 70. The brushes 56 and 58 are also formed of bristles rather than of a felt material; and this has a particular advantage since the rotating brushes interengage to provide for removal of chalk dust therefrom during the rotating movement. The use of a conventional felt eraser material is objectionable since chalk dust adheres to the felt material and is difficult to remove.

Fixed to the walls of the carriage housing and located beneath the gears 68 and is a baffle plate 69 that prevents chalk dust from entering the upper portion of the carriage housing, thereby protecting the motor 50 and drive assembly from excess accumulation of chalk dust thereon. In order to promote the removal of the chalk dust from the brushes 56 and 58, deflectors 71 and 73 are provided. The deflectors 71 and 73 are secured to the walls 32 and 34, respectively, beneath the baffle plate 69 and extend the length of the brushes. The brushes 58 and 56 strike the deflectors 71 and 73 during rotation thereof wherein chalk dust is deflected from the brushes and is directed toward the bottom of the carriage housing for collection, as will now be described.

In order to collect the chalk dust removed from the blackboard 10 by the brushes 56 and 58, a dust collecting device is provided and includes a dust collector housing 72 in which a dust bag 74 is located. A screen 76 is located in an opening in the upper wall of the housing 72 and filters air therethrough that escapes from the dust collecting system. The dust bag 74 communicates with a tube 78 that extends through an opening in the side wall 34 of the carriage housing and that has communication with a chamber 80 located directly below the brushes 56 and 58. Drivingly connected to the gear 82 mounted on the lower end of the shaft 60 of the brush 56 is a pinion gear 87 that is fixed to an impeller s aft 86. The impeller shaft 86 extends through a suitab e bearing fixed in the bracket 63, and in impeller 88 is mounted on the shaft 86 and is located within the chamber 80. It is seen that chalk dust removed from the blackboard 10 by the rotating brushes 56 and 58 is directed to the lower end of the carriage housing and into the chamber 80, the chalk dust being drawn therein by the impeller 88 which then propels the dust through the tube 78 and into the dust collecting bag 74. The housing 72 for the dust collecting bag 74 is conveniently removable from the carriage housing when the bag 74 is to be emptied or replaced.

The motor 50 is preferably of the small fractional horsepower type and normally is nonreversing. However, since it is necessary to reverse the movement of the carriage 20 after it has traversed the length of the blackboard 10, a unique drive assembly is provided that interconnects the output of the motor 50 to a drive 7 wheel for movement of the carriage in a first direction and then automatically provides for a change in the direction of the drive wheel for returning the carriage to the original or rest position. Referring now to FIGS. 1, 8 and 9, the shaft 67 is shown extending from the upper end of the motor 50 and has a drive pinion 92 mounted on the outer end thereof. Mounted on the shiftable operating rod 94 for lateral movement therewith and for selective driving engagement with the drive pinion 92 is a drive assembly generally indicated at 96. The drive assembly 96 includes a drive shaft 98 on the lower end of which a pinion gear 100 is located. The drive shaft 98 extends through a suitable bearing in the operating rod 94 and is received in a slot 97 formed in the cross bar 54. Also mounted on the drive shaft 98 is an intermediate gear 101, while the upper end of the drive shaft 98 extends through a bracket 103 and a friction drive wheel 102 is mounted for rotation therewith on the uppermost end of the drive shaft 98. The friction drive wheel 102 positively engages a vertical portion of the fixed rail 22 and provides the drive for the carriage with respect to the blackboard 11 during the operation of the automatic erasing device. Also interconnected to the bracket 36 is a stabilizing roller 105 that engages the rear portion of the bracket 36 in opposition to the drive wheel 102. As shown in FIG. 8, forward movement of the carriage 20 occurs when the motor 50 is drivingly interconnected to the drive wheel 102 through the drive pinion 92, pinion gear 100 and drive shaft 98.

In order to return the carriage 20 to the original or rest position, a counter-shaft 104 is provided and extends through the operating rod 94 for lateral move ment therewith and is received in a slot 106 formed in the cross bar 54. As shown in FIG. 9, rotation of the drive wheel 102 is reversed when the drive is directed thereto from the motor 50 and through the countershaft 104. In order to provide for this reverse rotation of the drive wheel 102, a pinion gear 110 is located at the lower end of the counter-shaft 104, and a transfer gear 112 is located at the upper end thereof in driving engagement with the intermediate gear 100. It is seen that when the drive assembly 96 is shifted laterally with the operating rod 94 as illustrated in FIG. 9, the drive pinion 92 moves into the driving engagement with the pinion gear 110 and the drive to the drive wheel 102 then occurs from the motor 50 through the countershaft 104 and gears 112 and 100.

In order to provide for the shifting movement of the drive assembly 96 through the operating rod 94, the operating rod 94 is mounted for lateral movement in the side walls 32 and 34 of the carriage housing and terminates at the outer ends thereof in pads 114 and 116. As described, the shafts 98 and 104 of the drive assembly 96 extend through the operating rod 94 and are laterally movable therewith. The lowermost ends of the drive shaft 98 and counter-shaft 104 extend through the slots 97 and 106, respectively of the bracket 54; and since sufficient space is provided in the slots 97 and 106, the drive shaft 98 and counter-shaft 104 is shiftable with the operating rod 94 for engagement of the drive pinion 92 with either the pinion gear 100 or the pinion gear 110.

As also shown in FIG. 1, the switch 52 includes the toggle lever 55 that is captured between spaced projections 120 formed on the underside of the operating rod 94. As the operating rod 94 is moved to the right as seen in FIG. 1, the toggle lever 55 of the switch 52 is shifted to the right to energize the motor 50. In this connection, the toggle lever 55 is of the spring operated type and is so designed as to shift to the opposite position when the carriage is reversed for continuing the operation of the motor 50. For this purpose the location of the toggle lever 55 of the switch 52 is disposed in an on" position when it is located in the right or in the left positions as seen in FIG. 1. When the toggle lever 55 is disposed in a center position, the switch 52 is in the neutral position and the motor is deenergized. On some occasions, it may be necessary to provide an extension for shifting the operating rod 94, particularly when a small child may not be able to reach the pad 116. For this purpose an elongated rod 122 is provided and is connected directly to the pad 116 and depends therefrom.

In operation of the automatic erasing device 10 as illustrated in the form of the invention shown in FIGS. 1 through 9, the device is placed in operation from a position of rest by depressing the pad 116 which forces the operating rod 94 to the right as seen in FIG. 1. This laterally shifts the drive assembly 96 therewith which moves the pinion gear 100 into engagement with the drive pinion 92 and establishes a direct drive from the motor 50 to the drive wheel 102. Simultaneously, the switch 52 is actuated to energize the motor 50; and as the drive wheel 102 is rotated, it drives through the frictional engagement thereof with the fixed rail 22 for moving the carriage 20 to the right as illustrated in FIG. 1. The motor 50 further rotates the brushes 56 and 58 which are in engagement with the blackboard 10, the brushes serving to erase the chalk markings on the blackboard. The chalk dust erased is drawn downwardly into the chamber for collection in the dust bag 74.

As the carriage 20 reaches the end of the blackboard 10, the pad 114 engages a stop 124 which forces the operating rod 94 to the left as illustrated in FIG. 1. The drive assembly 96 then shifts to the left to move the pinion gear 100 out of engagement with the drive pinion 92 and the pinion gear into engagement therewith. At the same time the toggle lever 55 of the switch 52 is shifted to the extreme left position which maintains the switch in the operative position and the motor 50 energized. The drive from the motor 50 is now directed to the drive wheel 102 by way of the countershaft 104 which reverses the direction of rotation of the drive wheel 102, and the carriage 20 is reversed and moves to the left as seen in FIG. 1. When the carriage 20 reaches the original or rest position thereof, the pad 116 engages a stop 126; but the operating rod 94 is prevented from returning to the forward operating position illustrated in FIG. 1 by an abutment 128 that is fixed to the side wall 34 of the' carriage housing. The abutment 128 permits the operating rod 94 to retract only to that position where the toggle lever 118 is located in the neutral position thereof, wherein the motor 50 is deenergized. The carriage is now located in the rest position, but can be reactivated upon movement of the operating rod 94 to the right as seen in FIG. 1 for the next erasing operation.

Referring now to FIGS. 10, 11 and 12, a modified form of the invention is illustrated and is directed to the reversing operation of the carriage and the manner in which the drive assembly 96 is operated to rotate the drive wheel 102. As seen in FIGS. 10 and 11, the motor 50 is mounted directly on an operating rod 128, on the outermost ends of which pads 130 and 132 are located. The brush shaft 60 is connected to the lower end of the shaft 67 of the motor 50 through the coupling 66 and The motor 50 is fixed to the operating rod 128 through brackets 133 and 134, suitable bolts 135 and 136 connecting the brackets 133 and 134 to the operating rod 128. A switch 138 having a lower toggle lever 140 extending therefrom is captured between projections 142 formed on the uppermost surface of the operating rod 128, the switch 138 thereby being actuated upon movement of the operating rod 128. The drive assembly 96 is substantially the same as that illustrated in FIGS. 8 and 9, except that the positions of the drive shaft 98 and the counter-shaft 104 are reversed from that illustrated in FIGS. 8 and 9. The shafts 98 and 104 are further mounted for rotation only and are not laterally shiftable; and for this purpose, the drive shaft 98 extends through a bearing 143 formed in a cross plate 144, while the counter shaft 104 extends through a similar bearing 145 formed in the cross plate 144. The shaft 90 of the motor 50 extends upwardly through the cross plate 144 and is movable laterally in a slot 146 formed therein.

In the operation of the invention illustrated in FIGS.

10, 11 and 12, the operating rod 128 is shiftable upon depressing of the pad 132 to the right which shifts therewith the motor 50 and the brush assembly 96 including the brushes 56 and 58. Upon shifting of the operating rod 128 to the right to the position illustrated in FIG. 11, the drive pinion 92 is moved to the right with the motor 50 for engagement with the pinion gear 100. Thus when the operating rod 128 is moved to the position illustrated in FIG. 11, the drive is accomplished from the motor 50 to the drive wheel 102 for moving the carriage in a traversing movement toward the right. When the carriage reaches the end of the blackboard, the pad 130 strikes the abutment 124 which forces the operating rod 128 to the left as seen in FIG. 11, wherein the motor 50 and the brushes 56 and 58 are returned to the position shown in FIG. 10.

In this position the drive pinion 92 engages the pinion gear 112, and the rotation of the drive wheel is reversed to return the carriage to the original or rest position. An abutment 150 is secured to'the wall 34 of the carriage housing and is engaged by the frame of the blackboard and thereby prevents the return of operating rod 128 to the operating position.'The switch 138 is thus moved to a neutral position for deenergizing the motor 50 after the carriage has reached the original or rest position thereof.

It is seen that the automatic erasing device embodied in the present invention traverses the blackboard in a forward and reverse direction with the brushes rotating in opposition to each other as driven by the motor 50. By providing the drive assembly 96, the brushes continue to rotate in the same direction as driven by the motor 50 even upon reverse or return movement of the carriage to the rest position. Thus, the reverse movement of the carriage is accomplished with a single motor and without the use ofa separate reversely operated motor.

While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims.

What is claimed is:

1. A device for automatically erasing a blackboard, comprising an elongated carriage extending at least the vertical dimension of said blackboard and located outwardly thereof in adjacent relation, means for mounting said carriage for movement in a direction that is longitudinal with respect to said blackboard for traversing the length thereof, brush means mounted in said carriage for rotating movement and engaging the surface of said blackboard, the longitudinal axis of said brush means being located parallel to the surface of said blackboard, motor means mounted in said carriage and interconnected to said brush means for producing the rotating movement thereof, a drive assembly adapted to be interconnected to said motor means and including drive means that is responsive to operation of said motor means for producing the movement of said carriage longitudinally of said blackboard, and for producing concurrent rotation of said brush means, and shiftable means mounted on said carriage for actuating said motor means and-for interconnecting said motor means with said drive means so that said carriage and brush means mounted therein are automatically moved longitudinally of said blackboard from a rest position and are returned to the rest position after traversing the length of said blackboard.

2. A device as set forth in claim 1, at least an upper rail located at the uppermost end of said blackboard, said drive assembly further including a friction wheel engaging said upper rail and interconnected to said drive means, wherein said drive means drives said friction wheel to produce the movement of said carriage.

3. A device as set forth in claim 1, said drive means including a drive shaft on which a drive wheel is mounted, said drive wheel engaging an elongated, fixed abutment in frictional contact for movement with respect thereto, a, counter-shaft located adjacent to and parallel with said drive shaft, said shiftable means for interconnecting said motor means with said drive means including an operating rod mounted on said carriage for transverse sliding movement with respect thereto, wherein said motor means is operatively engaged with said drive shaft and counter shaft in alternate relation for successively producing the traversal of said carriage longitudinally of said blackboard and the return thereof.

4. A device as set forth in claim 3, said fixed abutment including an elongated upper rail located at the uppermost end of said blackboard, spaced rollers interconnected to said housing and being received on said upper rail in rolling movement thereon for carrying said carriage in suspended relation with respect to said upper rail.

5. A device as set forth in claim 4 an elongated bottom rail located at the bottomost end of said blackboard in parallel relation to said upper rail, and roller means mounted on the lower portion of said carriage and engaging said lower rail for stabilizing said carriage during the movement thereof.

6. A device as set forth in claim 1, said drive means including a drive shaft on which a drive wheel mounted, a counter-shaft located adjacent to and parallel with said drive shaft and operatively connected thereto, said means interconnecting said motor means with said drive means including an operating rod that extends laterally through said carriage and that is movable transversely with respect to said carriage for connecting either said drive shaft or said counter-shaft to said motor means, and switch means responsive to movement of said operating rod for energizing said motor means.

7. A device for automatically erasing a blackboard, comprising an elongated carriage extending at least the vertical dimension of said blackboard and located outwardly thereof in adjacent relation, means for mounting said carriage for movement in a direction that is longitudinal with respect to said blackboard for traversing the length thereof, brush means mounted in said carriage for rotating movement and engaging the surface of said blackboard, the longitudinal axis of said brush means being located parallel to the surface of said blackboard, motor means mounted in said carriage and interconnected to said brush means for producing the rotating movement thereof, a drive assembly adapted to be interconnected to said motor means and including drive means that is responsive to operation of said motor means for producing the movement of said carriage longitudinally of said blackboard and for producing concurrent rotation of said brush means, and shiftable means mounted on said carriage for actuating said motor means for interconnecting said motor means with said drive means so that said carriage and brush means mounted therein are automatically moved longitudinally of said blackboard from a rest position and are returned to the rest position after traversing the length of said blackboard, said drive means including a drive shaft on which a drive wheel is mounted, said drive wheel engaging an elongated, fixed abutment in frictional contact for movement with respect thereto, a counter-shaft located adjacent to and parallel with said drive shaft, said shiftable means for interconnecting said motor means with said drive means including an operating rod mounted on said carriage for transverse sliding movement with respect thereto wherein said motor means is operatively engaged with said drive shaft and counter shaft in alternate relation for successively producing the traversal of said carriage longitudinally of said blackboard and the return thereof, switch means operatively engaging said operating rod and being electrically connected to said motor means, wherein movement of said operating rod when said carriage is in the rest position simultaneously energizes said motor means and interengages said motor means with said drive shaft for producing the traversing movement of said carriage and the rotating movement of said brush means.

8. A device as set forth in claim 7, said brush means including a pair of elongated brushes, the longitudinal axes of which are vertical, said brushes being operatively interconnected such that rotation thereof by said motor means produces counter rotation of one brush with respect to the other.

9. A device for automatically erasing a blackboard, comprising an elongated carriage extending at least the vertical dimension of said blackboard and located outwardly thereof in adjacent relation, means for mounting said carriage for movement in a direction that is longitudinal with respect to said blackboard for traversing the length thereof, brush means mounted in said carriage for rotating movement and engaging the surface of said blackboard, the longitudinal axis of said brush means being located parallel to the surface of said blackboard, motor means mounted in said carriage and interconnected to said brush means for producing the rotating movement thereof, a drive assembly adapted to be interconnected to said motor means and including drive means that is responsive to operation of said motor means for producing the movement of said carriage longitudinally of said blackboard and for producing concurrent rotation of said brush means, and shiftable means mounted on said carriage for actuating said motor means and for interconnecting said motor means with said drive means so that said carriage and brush means mounted therein are automatically moved longitudinally of said blackboard from a rest position and are returned to that rest position after traversing the length of said blackboard, said drive means including a drive shaft on which a drive wheel is mounted, a counter-shaft located adjacent to and parallel with said drive shaft and operatively connected thereto, said means interconnecting said motor means with said drive means including an operating rod that extends laterally through said cariage and that is movable transversely with respect to said carriage for connecting either said drive shaft or said counter-shaft to said motor means, and switch means responsive to movement of said operating rod for energizing said motor means, operating rod being interconnected to said drive shaft and counter-shaft, wherein transverse movement of said operating rod in a first direction produces a corresponding movement of said drive shaft and countershaft to locate said motor means in direct engagement with said drive shaft for effecting rotation thereof in one direction, and transverse movement of said operating rod in the opposite direction moves said drive shaft and counter-shaft therewith to locate said motor means in indirect engagement with said drive shaft through said counter-shaft for effecting rotation of said drive shaft in an opposite direction.

10. A device for automatically erasing a blackboard, comprising an elongated carriage extending at least the vertical dimension of said blackboard and located outwardly thereof in adjacent relation, means for mounting said carriage for movement in a direction that is longitudinal with respect to said blackboard for traversing the length thereof, brush means mounted in said carriage for rotating movement and engaging the surface of said blackboard, the longitudinal axis of said brush means being located parallel to the surface of said blackboard, motor means mounted in said carriage and interconnected to said brush means for producing the rotating movement thereof, a drive assembly adapted to be interconnected to said motor means and including drive means that is responsive to operation of said motor means for producing the movement of said carriage longitudinally of said blackboard and for producing concurrent rotation of said brush means, and shiftable means mounted on said carriage for actuating said motor means and for interconnecting said motor means with said drive means so that said carriage and brush means mounted therein are automatically moved longitudinally of said blackboard from a rest position and are returned to the rest position after traversing the length of said blackboard, said drive means including a drive shaft on which a drive wheel is mounted, a counter-shaft on which a drive wheel is mounted, a counter-shaft located adjacent to and paralleltwith said drive shaft and operatively connected thereto, said means interconnecting said motor means with said drive means including an operating rod that extends laterally through said carriage and that is movable means in direct engagement with said drive shaft for effecting rotation thereof in one direction, and transverse movement of said operating rod in the opposite direction moves said motor means therewith to locate said motor means in indirect engagement with said drive shaft through said counter-shaft for effecting rotation of said drive shaft in an opposite direction. 

1. A device for automatically erasing a blackboard, comprising an elongated carriage extending at least the vertical dimension of said blackboard and located outwardly thereof in adjacent relation, means for mounting said carriage for movement in a direction that is longitudinal with respect to said blackboard for traversing the length thereof, brush means mounted in said carriage for rotating movement and engaging the surface of said blackboard, the longitudinal axis of said brush means being located parallel to the surface of said blackboard, motor means mounted in said carriage and interconnected to said brush means for producing the rotating movement thereof, a drive assembly adapted to be interconnected to said motor means and including drive means that is responsive to operation of said motor means for producing the movement of said carriage longitudinally of said blackboard, and for producing concurrent rotation of said brush means, and shiftable means mounted on said carriage for actuating said motor means and for interconnecting said motor means with said drive means so that said carriage and brush means mounted therein are automatically moved longitudinally of said blackboard from a rest position and are returned to the rest position after traversing the length of said blackboard.
 2. A device as set forth in claim 1, at least an upper rail located at the uppermost end of said blackboard, said drive assembly further including a friction wheel engaging said upper rail and interconnected to said drive means, wherein said drive means drives said friction wheel to produce the movement of said carriage.
 3. A device as set forth in claim 1, said drive means including a drive shaft on which a drive wheel is mounted, said drive wheel engaging an elongated, fixed abutment in frictional contact for movement with respect thereto, a counter-shaft located adjacent to and parallel with said drive shaft, said shiftable means for interconnecting said motor means with said drive means including an operating rod mounted on said carriage for transverse sliding movement with respect thereto, wherein said motor means is operatively engaged with said drive shaft and counter shaft in alternate relation for successively producing the traversal of said carriage longitudinally of said blackboard and the return thereof.
 4. A device as set forth in claim 3, said fixed abutment including an elongated upper rail located at the uppermost end of said blackboard, spaced rollers interconnected to said housing and being received on said upper rail in rolling movement thereon for carrying said carriage in suspended relation with respect to said upper rail.
 5. A device as set forth in claim 4 an elongated bottom rail located at the bottomost end of said blackboard in parallel relation to said upper rail, and roller means mounted on the lower portion of said carriage and engaging said lower rail for stabilizing said carriage during the movement thereof.
 6. A device as set forth in claim 1, said drive means including a drive shaft on which a drive wheel mounted, a counter-shaft located adjacent to and parallel with said drive shaft and operatively connected thereto, said means interconnecting said motor means with said drive means including aN operating rod that extends laterally through said carriage and that is movable transversely with respect to said carriage for connecting either said drive shaft or said counter-shaft to said motor means, and switch means responsive to movement of said operating rod for energizing said motor means.
 7. A device for automatically erasing a blackboard, comprising an elongated carriage extending at least the vertical dimension of said blackboard and located outwardly thereof in adjacent relation, means for mounting said carriage for movement in a direction that is longitudinal with respect to said blackboard for traversing the length thereof, brush means mounted in said carriage for rotating movement and engaging the surface of said blackboard, the longitudinal axis of said brush means being located parallel to the surface of said blackboard, motor means mounted in said carriage and interconnected to said brush means for producing the rotating movement thereof, a drive assembly adapted to be interconnected to said motor means and including drive means that is responsive to operation of said motor means for producing the movement of said carriage longitudinally of said blackboard and for producing concurrent rotation of said brush means, and shiftable means mounted on said carriage for actuating said motor means for interconnecting said motor means with said drive means so that said carriage and brush means mounted therein are automatically moved longitudinally of said blackboard from a rest position and are returned to the rest position after traversing the length of said blackboard, said drive means including a drive shaft on which a drive wheel is mounted, said drive wheel engaging an elongated, fixed abutment in frictional contact for movement with respect thereto, a counter-shaft located adjacent to and parallel with said drive shaft, said shiftable means for interconnecting said motor means with said drive means including an operating rod mounted on said carriage for transverse sliding movement with respect thereto wherein said motor means is operatively engaged with said drive shaft and counter shaft in alternate relation for successively producing the traversal of said carriage longitudinally of said blackboard and the return thereof, switch means operatively engaging said operating rod and being electrically connected to said motor means, wherein movement of said operating rod when said carriage is in the rest position simultaneously energizes said motor means and interengages said motor means with said drive shaft for producing the traversing movement of said carriage and the rotating movement of said brush means.
 8. A device as set forth in claim 7, said brush means including a pair of elongated brushes, the longitudinal axes of which are vertical, said brushes being operatively interconnected such that rotation thereof by said motor means produces counter rotation of one brush with respect to the other.
 9. A device for automatically erasing a blackboard, comprising an elongated carriage extending at least the vertical dimension of said blackboard and located outwardly thereof in adjacent relation, means for mounting said carriage for movement in a direction that is longitudinal with respect to said blackboard for traversing the length thereof, brush means mounted in said carriage for rotating movement and engaging the surface of said blackboard, the longitudinal axis of said brush means being located parallel to the surface of said blackboard, motor means mounted in said carriage and interconnected to said brush means for producing the rotating movement thereof, a drive assembly adapted to be interconnected to said motor means and including drive means that is responsive to operation of said motor means for producing the movement of said carriage longitudinally of said blackboard and for producing concurrent rotation of said brush means, and shiftable means mounted on said carriage for actuating said motor means and for interconnecting said motor means with Said drive means so that said carriage and brush means mounted therein are automatically moved longitudinally of said blackboard from a rest position and are returned to that rest position after traversing the length of said blackboard, said drive means including a drive shaft on which a drive wheel is mounted, a counter-shaft located adjacent to and parallel with said drive shaft and operatively connected thereto, said means interconnecting said motor means with said drive means including an operating rod that extends laterally through said cariage and that is movable transversely with respect to said carriage for connecting either said drive shaft or said counter-shaft to said motor means, and switch means responsive to movement of said operating rod for energizing said motor means, operating rod being interconnected to said drive shaft and counter-shaft, wherein transverse movement of said operating rod in a first direction produces a corresponding movement of said drive shaft and counter-shaft to locate said motor means in direct engagement with said drive shaft for effecting rotation thereof in one direction, and transverse movement of said operating rod in the opposite direction moves said drive shaft and counter-shaft therewith to locate said motor means in indirect engagement with said drive shaft through said counter-shaft for effecting rotation of said drive shaft in an opposite direction.
 10. A device for automatically erasing a blackboard, comprising an elongated carriage extending at least the vertical dimension of said blackboard and located outwardly thereof in adjacent relation, means for mounting said carriage for movement in a direction that is longitudinal with respect to said blackboard for traversing the length thereof, brush means mounted in said carriage for rotating movement and engaging the surface of said blackboard, the longitudinal axis of said brush means being located parallel to the surface of said blackboard, motor means mounted in said carriage and interconnected to said brush means for producing the rotating movement thereof, a drive assembly adapted to be interconnected to said motor means and including drive means that is responsive to operation of said motor means for producing the movement of said carriage longitudinally of said blackboard and for producing concurrent rotation of said brush means, and shiftable means mounted on said carriage for actuating said motor means and for interconnecting said motor means with said drive means so that said carriage and brush means mounted therein are automatically moved longitudinally of said blackboard from a rest position and are returned to the rest position after traversing the length of said blackboard, said drive means including a drive shaft on which a drive wheel is mounted, a counter-shaft on which a drive wheel is mounted, a counter-shaft located adjacent to and parallel with said drive shaft and operatively connected thereto, said means interconnecting said motor means with said drive means including an operating rod that extends laterally through said carriage and that is movable transversely with respect to said carriage for connecting either said drive shaft or said counter-shaft to said motor means, and switch means responsive to movement of said operating rod for energizing said motor means, said operating rod being interconnected to said motor means, wherein transverse movement of said operating rod in a first direction produces a corresponding movement of said motor means to locate said motor means in direct engagement with said drive shaft for effecting rotation thereof in one direction, and transverse movement of said operating rod in the opposite direction moves said motor means therewith to locate said motor means in indirect engagement with said drive shaft through said counter-shaft for effecting rotation of said drive shaft in an opposite direction. 